Gelled nitric acid rocket propellant containing silica gel



nite States The invention described herein may be manufactured and usedby or for the Government for governmental purposes without the paymentto us of any royalty there- This invention relates to rocket propellantsand more particularly concerns new compositions of matter having gelledor grease-like structures comprising silica gel and rocket fuels and/ oroxidizers.

Rocket fuels and oxidizers, in liquid form among others, are currentlyemployed as propellants in space vehicles. It is desirable under sometypes of operating conditions to employ the liquid materials in a solid,grease-like or semi-solid form. For example, when gelled materials areused, the seal problem inherent in liquid propellant rockets andmissiles is eliminated, and hence, such vehicles could be fueled aconsiderable period in advance. The gelled material lends itself to easypumping and further, the foaming problem is not encountered when gelledmaterials are pumped through small orifices as are liquids.

Heretofore, gelling agents for liquid fuels and oxidizers have beenknown in the art, but in general, have failed to meet the stringentrequirements of rocket and missile devices. For the most part, knowngelling agents have been inadequate in that gels could not be formulatedfrom liquid hydrocarbons, for example, of diverse boiling ranges and/ ordiverse compositions by simple stirring or mixing of the gelling agentat ambient temperatures. They have been unsatisfactory for theadditional reason that their rate of gelling hydrocarbon liquids isgreatly affected by the temperature of admixing. Also, they were notcapable of forming satisfactory gels within a reasonable time whenreasonable amounts are added to such hydrocarbon mixtures as aviationfuels containing substantial amounts of isooctane.

Nitrocarbons are also commonly employed as propellant. Up to now,difiiculty has been encountered when an attempt was made to produce gelsfrom the various liquid nitrohydrocarbons, and particularlynitroparafiins, without seriously aifecting the oxygen balance andotherwise changing their properties.

The present invention overcomes these and other difiiculties involved ingelling liquid fuels and oxidizers by providing compositions comprisingliquid propellants which are gelled by minor additions of finely dividedsilica gel, said gels retaining their consistency for long periods oftime without undergoing deleterious changes in properties.

It is therefore a primary object of this invention to provide a gelledor grease-like composition comprising minor proportions of a gellingagent which may be incorporated into a wide variety of liquid fuels andoxidizers by simple mixing or stirring at ambient temperatures.

Another object of the invention is to provide compositions whereby agelling agent is incorporated into a wide variety of liquid fuels andoxidizers to produce stable gels for rocket and missile propellants.

An additional object of the invention is to provide compositions ofgelled fuels and oxidizers which have incorporated therein a gellingagent which is inexpensive, readily available and easy to use; andwherein the resulting composition is not susceptible to prematurebreakdown with concomitant loss of viscosity.

Other and further objects of the invention will be apparent to thoseskilled in the art upon study of this disclosure.

Various liquids and liquid combinations have been found useful as rocketpropellants. Some propellants consist of a single material, and aretermed monopropellants. Those propellants involving two materials aretermed bipropellants and normally consist of an oxidizer and a fuel.

Nitromethane, among others, is a well known mono- -propellant. Wellknown bipropellants include hydrogen peroxide or liquid oxygen as theoxidant with a fuel component such as ethanol-water, ammonia, hydrazine,or hydrogen; and nitric acid as the oxidizer with aniline or alcohols asthe hypergolic fuel component.

When employing a concentrated white fuming nitric acid, e.g., having aconcentration in the neighborhood of about to as the oxidizer in arocket propellant, it is often necessary, dependent on the specific fuelcomponent, to make ignition more prompt by dissolving minor proportionsof nitrogen dioxide in the white fuming nitric acid, thereby forming redfuming nitric acid.

Other fuels such as alkyl nitrates, of which ethyl, propyl and butylnitrates are the most common, and nitroparaffins, such as nitromethane,and nitroethane, may be readily gelled in accordance with thecompositions claimed by this invention. Alcohols, such as ethanol,propyl alcohol and butyl alcohol, and hydrazines, for example,monomethyl hydrazine, and combinations including hydrazine and ethylenediamine, hydrazine and alcohols as aforementioned, hydrazine andammonia, with unsymmetrical dimethyl hydrazine, and unsymmetricaldimethyl hydrazine with diethylene triamine have also been foundamenable to gellation in accordance with the compositions of the presentinvention. Mixtures or blends of any of the aforedescribed alkylnitrates and alcohols, of nitroparaffins with alkyl nitrates and/oralcohols; and alcohols mixed with nitroparafiins, aniline and hydrazine;and amines, such as diethylene triamine,NNNN-tetramethyl-butane-l,3-diamine, trimethylamine and aniline; andhydrocarbons such as isooctanes have also been successfully gelled asclaimed herein.

Finely divided, inorganic, commercially available silica gel is used asthe sole gelling agent. The material is cheap and easy to use. Three tofive weight percent of this material is slowly added to any of theliquid fuels, fuels and oxidizers, or any of the prescribed operablecombinations thereof, at room or ambient temperature, the liquid beingstirred during addition. The stirring may be accomplished by hand, oroptionally, if larger amounts are involved, by any suitable orconventional mechanical stirrer or agitator. The stirring operation isnormally performed within 1 to 2 minutes, no further agitation beingnecessary thereafter. At the upper limit of silica gel addition, i.e.,about 5%, the liquid may partake of a semi-grease-like structure, orthick gel, while further additions up to about 8% will progressivelyresult in the formation of a grease-like compound. The gelled orgrease-like compositions have been found to remain stable and yet retaintheir approximate viscosity for periods upwardly of six months, underusual military storage conditions.

By way of further explanation, some specific examples illustrating theinvention will hereinafter be described. This is done solely by way ofexample and is intended neither to delineate the scope of the inventionnor limit the ambit of the appended claim:

Example I Ninety-six pounds of monomethyl hydrazine was contained in asuitable vat and agitated mechanically. Four Kr pounds of finely dividedsilica gel Was poured slowly thereinto consuming about 30 seconds, theagitation continuing throughout. Agitation Was further continued forabout 90 seconds, the entire operation'being performed at 78 F. A stablegelled fuel resulted.

Example II Twenty-three pounds each of propyl nitrate and nitroethanewere mixed for 30 seconds until the compounds were thoroughly blended.While the mixing continued 3.8 pounds of finely divided silica gel wasslowly added thereintq. Additional agitation for approximately 60seconds at 75 F. produced a stable gel composition having thecharacteristics desired for rocket propellants.

It is apparent that we have provided a wide variety of rocket propellantcompositions in gelled, semi-grease or grease-like forms and dependingonly upon the amount of gelling agent employed. The resultingcompositions are stable, exhibiting shelf lives upwardly of six monthswithout undesirable settling out or loss of viscosity. An

important feature of the present invention resides in the smallproportions of gelling agent necessary for any of the prescribedmaterials discussed hereinabove, i.e., a minimum of about 3 weightpercent of agent ordinarily produces a gel-like compound Whileincreasing the silica gel content to about 8 weight percent results in agrease- References Cited in the file of this patent UNITED STATESPATENTS 2,891,852 Schaad June 23, 1959 2,902,351 Stokes Sept. 1,19592,922,703 Bauer Jan. 26, 1960 3,035,950 Long -c May 22, 1962 3,077,072Rice Feb. 12, 1963 OTHER REFERENCES Zimmerman et al.: Handbook ofMaterial Tradenames, Supplement II, p. 40 (1957), Industrial ResearchService Inc., Dover, New Hampshire.

